Collaborative Research: Systematic Comparisons of Regular and Slow Earthquakes in Central and Southern California

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Nontechnical This project aims to understand different behaviors of regular and slow earthquakes in Central and Southern California. The recent discovery of slow earthquakes broadens our view on how active faults relieve tectonic stresses. By applying various techniques to extensive seismic data collected by EarthScope and other permanent networks, the Principal Investigators (PIs) are creating better images of detailed fault zone structures within and below the depth where regular earthquakes occur. The PIs also hope to better understand how fault zone properties control different fault slip behaviors (regular vs slow). The project will improve our estimation of when and where large earthquakes occur and help to evaluate future seismic hazards. Because slow deformation may occur before large earthquakes, better tracking slow earthquakes could also help to better understand the processes relevant to how earthquakes initiate and interact. The PIs are developing new tutorials on triggering and detection of regular and slow earthquakes from seismic data. In addition, they are developing products to visualize and hear seismic data relevant this project. All these activities help to attract next generation scientists into the seismological field, and train them with state-of-the-art tools so that they can succeed in their future careers. This project also supports training of two graduate students and an international collaboration with Japanese researchers.Technical The newly discovered deep tectonic tremor and accompanying slow-slip events have changed our view on how accumulated tectonic stresses are released through fault movement below the seismogenic zone. Deep tremor has been clearly observed along the Parkfield-Cholame section of the San Andreas Fault (SAF) in Central California since around the time when the Earthscope project started more than 15 years ago. However, except a few cases, tremor has not been ubiquitously found along the San Jacinto Fault (SJF) and other major faults in Southern California. Although progress has been made to further understand the physical mechanisms for tremor and regular earthquakes, many fundamental questions remain open. These include: 1. What are the primary factors that control different tremor and microearthquake behaviors in Central and Southern California? 2. How do tremor and low-frequency earthquakes (LFEs) differ from regular earthquakes? 3. What are in situ fault zone properties at depth where regular and slow earthquakes occur? To answer these questions, the PIs are conducting a systematic analysis of regular and slow earthquakes in Central and Southern California using state-of-the-art techniques and available dataset in these regions. Specifically, the PIs are performing the following research tasks: 1. Detect and relocate microearthquakes along the Parkfield section of the SAF and along the SJF in Southern California; 2. Better detect and locate tremor and LFEs along the SJF in Southern California and compare their behaviors with those in Central California; 3. Quantify the triggerability of microearthquakes and tremor/LFEs in these regions; and 4. Delineate internal fault zone structures using Vp/Vs ratios and other imaging methods.The project goal is to obtain highly accurate locations of microearthquakes and LFEs in both regions, and use them to study their responses to external stress perturbations, and obtain in situ fault zone properties that control different behaviors of regular and slow earthquakes in Central and Southern California. In addition, the PIs are continuing their development of online tutorials on earthquake triggering and detection, and visualization and sonification products related to Earthscope. These activities help to educate general audience with frontier earthquake science, attract next generation scientists into the seismological field, and train them with state-of-the-art tools so that they can succeed in their future careers. This project also supports training of two graduate students and an international collaboration with Japanese researchers.